Flight Narita International Airport departs from Tokyo Narita International Airport at 14:00 and arrives at Seoul Incheon International Airport at 16:45.
The flighttime is about 2h 45m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 565 Km.
The best day to arrive at Tokyo is Tuesday and it would be best to avoid Sunday, as prices are on average 98.05% higher than on Tuesday. (Average prices, based on 4216840 datapoints.)
We have a lot more statistics for flights 7C 1104 and between Tokyo and Seoul.
